Acute alterations of urinary and serum calcium in normal volunteers were analyzed following low (8 gm) and high protein (24 gm) load with low (350 mg) and high (1000 mg) oral calcium supplements. Two hours following an acute oral load of 350 mg or 1000 mg of calcium, serum calcium rose to an average of 0.23 mg/d1 and 0.88 mg/d1, respectively. Urinary calcium increased one to two hours after the load and averaged 0.104 mg/mg Cl and 0.035 mg/mg Cr following the low and high calcium loads. With a protein load, urinary calcium rose to greater degree when protein was added to the low calcium load than when added to the high calcium load. There were inconsistent changes in titratable acid or ammonia production noted. In some patients with nephrolithiasis, it was possible to control the urinary loss of calcium by altering dietary protein with Ca intake constant at 400-500 mg/day.